<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>二列布局</title>
    <style type="text/css">
        .mian {
            width: 800px;
            margin: 0 auto;/*让块居中*/
        }

        .left {
            background: blue;
            width: 20%;
            height: 600px;
            float: left;/*靠左浮动*/
        }
        .zhong{
            background:yellow;
            width: 30%;
            height: 600px;
            float: left;
        }

        .right {
            background: red;
            width: 50%;
            height: 600px;
            float: right;/*靠右浮动*/
        }

    </style>
</head>
<body>
<div class="mian">
    <div class="left"></div>
    <div class="zhong"></div>
    <div class="right"></div>
</div>


</body>
</html>